In a multi-cylinder type internal combustion engine, an apparatus for supplying an air-fuel mixture is provided to supply the air-fuel mixture to each cylinder. Such an air-fuel mixture supplying apparatus is known and is shown in FIG. 6. In FIG. 6, reference numeral 2 denotes an internal combustion engine; 4 indicates an air cleaner; 6 a throttle body; and 8 an intake manifold. Air which passes into an intake passageway 10 on the downstream side of the air cleaner 4 is mixed with fuel which is supplied from a fuel injection valve 26 and an air-fuel mixture is obtained. The flow rate of the air-fuel mixture is adjusted by a movable throttle valve 14 provided in a throttle body intake passageway 12, and thereafter the air-fuel mixture flows into a collecting passageway 18 of a collecting pipe 16 which is part of the intake manifold 8. The air-fuel mixture flowing through the collecting passageway 18 is respectively branched into a branch passageway 22 of a branch pipe 20 which is branched from the collecting pipe 16 for distribution into each cylinder 24 of the internal combustion engine 2.
However, in such an air-fuel mixture supplying apparatus, the air and the air-fuel mixture can not be properly mixed at low temperatures, particularly at super low temperatures, so there is a problem in that it is difficult to distribute and supply uniform fuel into each cylinder. Therefore, air-fuel mixture supplying apparatuses as disclosed in Japanese Patent Application Laid-Open No. 107054/1980, Japanese Utility Model Application Laid-Open Nos. 49545/1982 and 61476/1985, and the like have been proposed. Such an apparatus is also disclosed in Japanese Patent Application No. 46414/1988 as owned by the assignee of this invention. According to the above apparatuses, as shown in FIGS. 2-5, a pipe member 32 projects transversely into the collecting passageway 18 to create a partition or shroud. This pipe member 32 forms an installation passageway 30 whose inlet end communicates with the discharge end of the intake passageway 12 and whose outer end opens into the collecting passageway 18. This passageway 30 thus effectively acts as an extension of the passageway 12. An auxiliary air passageway 34 which bypasses the throttle valve 14 is provided for introducing auxiliary air downstream of the throttle valve.
More specifically, according to the apparatus disclosed in Japanese Patent Application Laid-Open No. 107054/1980, as shown in FIG. 3, an auxiliary air outlet 52 at the downstream end of the auxiliary air passageway 34 is annularly formed around the whole periphery of the discharge end opening of the passageway 30 so that air and fuel are mixed in the collecting passageway 18. On the other hand, according to the apparatus disclosed in Japanese Utility Model Application Laid-Open No. 49545/1982, as shown in FIG. 4, a plurality of auxiliary air outlets 52 are associated with the auxiliary air passageway 34 and are formed circumferentially around the passageway 30 radially through the wall surface 54 of the pipe member 32, thereby preventing fuel from being deposited onto the wall surface 54. Further, according to the apparatus disclosed in Japanese Utility Model Application Laid-Open No. 61476/1985, as shown in FIG. 5, the auxiliary air outlet 52 of the auxiliary air passageway 34 is formed in the wall of the collecting passageway 18 outside the base end portion of the pipe member 32, thereby preventing choking of the auxiliary air outlet 52.
Further, according to the apparatus of Japanese Patent Application No. 46414/1988, as shown in FIG. 2, the auxiliary air outlet 52 of the auxiliary air passageway 34 is formed in the wall surface 54 near the end opening of the passageway 30 in a manner such that the end port of passageway 34 opens directly through the open lower end of passageway 30. The outlet 52 is directed so as to have a first directional component along the axial centerline direction A in the downstream direction of the passageway 30 and a second directional component along the axial centerline direction B in the downstream direction of the passageway 18. The air and the fuel are mixed in the passageway 30. Reference numeral 28 denotes a nozzle as a fuel supplying mechanism.
However, according to the apparatus disclosed in Japanese patent Application Laid-Open No. 107054/1980 (FIG. 3), since the auxiliary air outlet 52 is annularly formed around the whole periphery of the end opening of the passageway 30, the auxiliary air is introduced in parallel with the air-fuel mixture flowing into the collecting passageway 18. On the other hand, according to the apparatus disclosed in Japanese Utility Model Application Laid-Open No. 49545/1982 (FIG. 4), since the auxiliary air outlets 52 are formed circumferentially of the passageway 30 through the wall surface 54, the auxiliary air is introduced substantially in parallel with the air-fuel mixture along the wall surface 54 of the passageway 30. Further, according to the apparatus disclosed in Japanese Utility Application Laid-Open No. 61476/1985 (FIG. 5), since the auxiliary air outlet 52 is formed in the wall of passageway 18 outside the base end portion of the pipe member 32, the auxiliary air is introduced into the collecting passageway 18 separately from the air-fuel mixture. Further, according to the apparatus of Japanese Patent Application No. 46414/1988 (FIG. 2), the air discharged from the auxiliary air passage 34 is not effectively mixed with the air-fuel mixture in the passageway 30 but rather is directly introduced into the collecting passage 18, whereupon some of this unmixed air is directly introduced into one or more of the branch passageways 22 so that the air-fuel mixture in the respective cylinder becomes lean.
As mentioned above, according to the above apparatuses, the air and the fuel are not actively mixed in the passageway 30 and a thoroughly mixed air-fuel mixture is not actively supplied to the downstream side of the collecting passageway 18. Therefore, a uniformly mixed air-fuel mixture can not be distributed to each cylinder of the internal combustion engine, and there thus is an inconvenience in that the starting performance at low temperatures, particularly at super low temperatures, is lost. Another undesirable occurrence is that fuel which is not properly mixed with air collects on the bottom surface of the collecting passageway 18, so that stability in idling is lost.
Therefore, the objects of the present invention include providing an apparatus for supplying an air-fuel mixture in an internal combustion engine in which air and fuel can be actively mixed in a collecting passageway of an intake manifold collecting pipe, in which any fuel which is not properly mixed with air can be actively fed in the downstream direction of the collecting passageway, in which the uniformly mixed air-fuel mixture can preferably be distributed to each cylinder of the internal combustion engine, and in which starting performance at low temperatures and idling stability can be improved.